1. Field of the Invention
The present invention relates to a wide-range air/fuel ratio sensor for performing the accurate detection of the air/fuel ratio over a wide measurement range and also to a detector using the same.
2. Description of the Related Art
Sensors capable of continuously measuring the air/fuel ratio of the exhaust gas from vehicles such as motor cars and the like over a wide measurement range and which can be mass-produced with their reduced dimensions have been developed recently from the sintered green sheet technique and film printing technique. Such sensors includes a limiting current type oxygen sensor having an atmosphere reference (disclosed in Japanese Patent Application No. 56-123373), a wide-range air/fuel ratio sensor comprising, in combination, an oxygen concentration cell type element and an oxygen pump element (disclosed in Japanese Patent Application No. 58-237626 and "Sensor and Actuators", 2 (1982), pages 371-384) and so on. There is also known an integral sensor unit comprising a combination of a limiting current type oxygen sensor having an alumina substrate not exposed to the ambient air with a resistance-variable type .lambda.=1 sensor, the integral sensor unit adapted to measure the air/fuel ratio in the range from .lambda.=1 to the fuel lean region (U.S. Pat. No. 4,661,234). All these sensors are adapted first to measure the amount of oxygen in the exhaust gas and then to detect the air/fuel ratio therein from the measured results of the oxygen.